This invention relates to a device and a method for measuring the dynamic pressure in the combustion chamber of, for example, a gas turbine machine.
As part of the monitoring controls and diagnostic tools for an operating combustion system in a rotary machine such as a gas turbine, it is necessary to measure and acquire various data including combustion chamber dynamic pressure. This data is used to confirm proper operational health of the combustion system, and is also used to tune the gas turbine engine so that it is operating with an appropriate balance between combustion dynamics and emissions. Measuring dynamic pressure directly in a combustion chamber requires a sensor that functions in operating environments having temperatures in the range of 2000-3000° F. Currently, existing dynamic pressure probes are designed to withstand no more than about 1000° F. As a result, existing combustion dynamic pressure measurement methods do not utilize sensors located directly in the combustion chamber. Rather, current systems use metal tubing called wave guides to transmit the pressure signal from the combustion chamber to a remotely located dynamic pressure sensor. The factors that affect the degree of signal attenuation for these systems include the following:    1. The internal diameter of the tubing.    2. The length of the tubing.    3. The temperature profile within the tubing.    4. The static pressure within the tubing.    5. The frequency content of dynamic pressure signature.
With these systems, a damping coil wound around a horizontal axis is used to prevent the formation of standing waves in the measurement system. This type of system, however, results in the formation of condensate in the horizontal wound damping coil. Condensation build up in the coils results in standing waves being formed in the tubing which attenuates the true source signal and prevents it from being measured accurately. To overcome this problem, current systems have to be periodically purged to remove the condensate from the damping coils.
In addition, the long length of the metal tubing from the combustion chamber to the remotely located sensor results in significant attenuation of the pressure signal, and thus it is not possible to measure the true dynamic pressure of the combustion system with this approach. The signal attenuation resulting from this type of system increases as the frequency of the signal being measured increases.
Accordingly, a probe holder is needed that isolates the dynamic pressure sensor from the temperature of the combustion chamber, while still allowing the sensor to observe in a more accurate manner the dynamic pressure characteristic of the combustion chamber. In other words, this needs to be done in a manner which will not introduce any standing waves, resonances or signal attenuations of the combustion chamber dynamic pressure signals, and that will not result in the formation of condensation in the measurement system.